Objective mount with built-in filters



July 27, 1954 |-||NDEN 2,684,611

I OBJECTIVE MOUNT WITH BUILT-IN FILTERS Filed Feb. 12, 1952 3 Sheets-Sheet l Fig.7

INVENTOR. m/rz film DEN y 27, 5 F. HINDEN OBJECTIVE MOUNT WITH BUILT-IN FILTERS 3 Sheets-Sheet 2 Filed Feb. 12, 1952 INVENTOR. Pn rz HINDI BY July 27, 1954 F. HINDEN 1 2,684,611

OBJECTIVE MOUNT WITH BUILT-IN FILTERS Filed Feb. 12, 1952 s Sheets-Sheet s Fig. 10 w Patented July 27, 1954 OBJECTIVE MOUNT FILTE WITH BUILT-IN RS Fritz Hinden, Aarau, Switzerland Application February 12, 1952, Serial No. 271,145

12 Claims.

This invention relates to mounts for photographic objectives with built-in filters selectively movable into positions concentric with the optical axis of the objective.

As is well known, photographic pictures can be appreciably improved in certain instances by employing filters with different colors or hues in accordance with the desired efiect.

It is already known to mount such filters in mounts which can be fitted or threaded upon the camera objective. However, such an arrangement is inconvenient and time-consuming in particular when sun shades are simultaneously used which generally must be removed before the filter mounts can be attached.

To facilitate the carrying, fitting, and exchange of filters, it has been proposed to arrange the filters in a circle on a disc eccentrically rotatable about the optical axis of the objective so that by rotation of this disc difierent filters can be moved into the position of use in the manner of the different diaphragm openings of a diaphragm of the revolving type. The difliculty with such an eccentric disc is that it requires considerable space and that the lens barrel or mount of the objective must have an abnormally large outer diameter when the disc is to be disposed entirely within the objective mount. With eccentric discs of this type one of the openings is not occupied by a filter so that pictures without use of a filter can be taken when this opening is in alignment with the objective axis. However, the disadvantage of this arrangement is that in certain instances the photographer must rotate all the filters past the objective before he reaches the opening without a filter.

One of the objects of the present invention is to provide an objective mount with built-in filters which permits moving any one of these filters into its operative position, that is, into the position concentric with the optical axis without necessitating an inconvenient and unsightly increase in the outer configuration of the mount and without requiring a repeated or time-consuming manipulation of the filters before either the desired filter is placed in position of use or no filter is in front of the objective.

According to the invention, the aforementioned and other objects, features and advantages of the invention are attained by providing two rings, one fixed and the other rotatable, within the mount in positions concentric with the optical axis of the objective and by pivotally supporting a plurality of the filter carriers on one of said rings in positions circumferentially spaced about the optical axis of the objective. Each of the filter carriers is operatively coupled with control means which are controlled by the relative rotational position of the two rings so that any one of the filter carriers can be pivoted either into a position concentric with the optical axis of the objective or into a position outside the incident light beams passing through the objective.

According to a now preferred embodiment of the invention, each of the filter carriers pivotally supported on one of the rings is provided with a guide pin which guide pins engage a guiding groove in the other ring. This guiding groove is generally in the form of a circle concentric with the optical axis but includes a flattened or otherwise radially bent-in section. The filter carriers and their guide pins are disposed in a spatial relationship with the guiding groove so that a filter carrier the guide pin of which engages said flattened groove section, particularly the center thereof, is pivoted in a position concentric with the optical axis whereas all the other filter carriers the guide pins of which engage the circular section of the guiding groove are pivoted in a position in which they are located outside the incident light beams through the objective, the positions of the guide pins in the guiding groove and, hence, of the filter carriers relative to the optical axis being controlled by a rotation of the rotatable ring.

The center angle defined by the ends of the flattened groove section is preferably so selected that a filter carrier is moved completely from its operative position concentric with the optical axis into its'inoperative position before one of the adjacent filter carriers reaches the flattened groove section and begins to move toward its operative position when the two rings are rotated relative to each other. The two rings are preferably provided with detents, more specifically, twice as many detents are preferably provided than there are filter carriers so that there is a detained position of the two rings in which none of the filter carriers is in the operative position between each two relative positions of the two rings, as determined by one of the dentents, in which one of the filter carriers is in position of use.

It is advantageous to support the filter carriers on the support ring or barrel of the objective and to provide the guiding groove in a filter carrier setting ring which is rotatably mounted on the support ring for the objective.

As is well known, each filter carried by one of the carriers absorbs a certain amount of light.

Consequently, when a filter is used the exposure time must be increased in accordance with the amount of light absorbed by the respective filter. In other words, the opening of the objective is in effect reduced. The period of time by which the exposure time must be increased when a filter is employed is sometimes referred to as the time extension factor of the filter. It was hitherto necessary to ascertain this time extension factor from a table and then to take the same in account when the exposure time is calculated. This additional operation causes frequently mistakes in the calculation of the exposure time.

According to another object of the invention the aforementioned additional operation is eliminated by providing filter setting indicia on the ircumference of the filter setting ring which indicia indicate which one of-the filters is in its operative position and serve sim ltaneously as a marker for a diaphragm setting ring with a diaphragm scale thereon. These indicia, in addition. to the actually set opening of the diaphragm, show on the diaphragm scale of the diaphragm setting ring the diaphragm opening reduced by a value corresponding to the time extension factor of the filter placed in the position of use. As previously explained, it is this reduced opening or" the diaphragm which must be taken in account to obtain the correct exposure time.

Other and further objects, features and advantages of the invention will be pointed out hereinafter and set forth in the appended claims forming part of the application.

In the accompanying drawing several now preferred embodiments of the invention are shown by of illustration and not by way of limita- "on.

in the drawings:

Fig. l is a side view, partly in section, of an objective mount equipped with four filters mounted for selective setting.

Fig. 2 is a front view of the filters and the means for supporting and setting the same, as seen from the side of the camera.

Fig. 3 is a plan view of the support ring of the objective mount, as seen in the direction of the incident light.

i is a section taken on line A-A of 3.

Fig. 5 is a plan view of the notch ring of the diaphragm of the objective, as seen from the side of the camera.

6 is a section taken on line B--}3 of 5.

Fig. 7 is a plan view of one of the leaves of the diaphragm on an enlarged scale.

Fig. 8 is a side view of Fig. 7.

Fig. 9 is a modification oi the setting indicia of the means for setting the filters.

Fig. 10 is a side view, partly in section, of a modification of an objective mount equipped with means according to the invention for selective setting of filters, and

Fig. 11 is a front view of the filters and the means for supporting and setting the same according to Fig. 10, as seen from the side of the camera.

Referring now to the figures in detail, the exemplified objective mount comprises an objective support ring 4 which forms an externally threaded flange 2 on its side facing the camera. The ring is provided with an annular groove 1 on the side of the incident light. On the same side ring is flanged to form a ring portion of reduced diameter. Ring portion is provided with an internal thread i into which a iocussing or distance setting ring or lens barrel 5 can be threaded. The objective proper comprises three lens components L1, L2 and L3. Component L1 is mounted in ring 5 on the camera side thereof; component L2 is held by a bearing ring member s of ring I; and component L3 is mounted in a ring member 3 threaded in ring I. A ring 8 is fitted upon the inner portion I of ring I. As can best be seen on Fig. 1, ring portion I which protrudes axially beyond an outer portion I" of ring I supports a ring 8 secured upon the inner ring portion I of ring I against rotation and axial displacement by means of a screw H3 screwed in a threaded bore 9 extending vertically relative to the axis of the objective mount. Ring is has thereon a focussing mark II which cooperates with a range scale provided on the adjacent cylindrical surface I2 of the focussing ring 5. Between the lens components L1 and L2, there is disposed a diaphragm of the iris type the leaves It of which are pivotally mounted by means of a pivot I i to a support ring id for the diaphragm which ring has an angular profile as can best be seen on Fig. 1. This ring I5 is fitted in the rear end of the inner portion I of ring I and secured in portion I against axial displacement and rotation by means or a screw It. The leaves It of the diaphragm are pivoted by means of a notched ring Il which has also an angular profile. Ring Il is provided on its side juxtaposed to the support ring I5 for the diaphragm with notches I8, one for each leaf I3. Each leaf is guided in the respective notch I8 by means of a bolt I9. The notch ring ii is rotatably mounted in the support ring I5 and provided with a flange portion Il' protruding beyond ring It. This ring portion H includes a radially extending threaded bore in which is threaded a screw bolt 28. Bolt 29 is fitted in a transverse slot 2i in the inner portion i of ring I. This transverse slot occupies approximately one-third of the circumference of inner ring portion I. Bolt 29 is further held in a longitudinal slot 2.2 in the rear end of a ring 23 for adjustment of the diaphragm opening. Ring 23 is rotatably mounted upon the inner ring portion l of ring i so as to abut against ring 8 and also to protrude over the same. The portion of ring 23 protruding over ring 8 is provided at a point of its circumference with a radially directed bore 25 through which screw it can be inserted which, as previously mentioned, serves to secure ring 5; upon the inner portion I of ring i.

The spacing of notches IS of the notch ring I! and the configuration or" leaves is are so selected that the individual calibration lines of the diaphragm scale provided on a conical annular surface 25 of the diaphragm setting ring 23. are equally spaced. Diaphragm setting ring 23 has in the cylindrical surface with which it. is seated upon the inner ring portion I of ring I a bore 23 ending within the ring material. A ball 28 guided in bore 26 is engageable' by the action of a loaded spring 2? with detents 2a in the circumference of the inner ring portion I of ring I, one detent '29 being provided for each scale marking of the diaphragm scale. As a result,

1 the diaphragm setting ring 2 3 is retained by the respective detent in each position corresponding to one of the calibration markings of the diaphragm scale.

As can best be seen on Figs. 3, and 4, four bores 36a, 30b, 30c and 3M extend parallel to the axis of the objective from the base of annular groove 3 of ring I. In each of these bores, there is journalled a pivot pin 32a, 32b, 32c and'SZd respectively secured to the knee of a filter carrier 3la, 3lb, Me and 3Id in the form of a bell crank lever the configuration of which can best be seen on Fig. 2. The longer arm of each bell crank is bent twice at a right angle and reaches through a slot 33a, 33b, 33c and 33d respectively in the base of annular groove 3 of ring I and also through corresponding openings 33a, 33b, 33c and 33d respectively of the mounting ring 6 into the space between the mounting rings 5 and l and between the lens components L2 and L3 respectively. The end of the longer arm of each filter carrier 31a, 31b, 3l'c and 3|d supports one of four different filters 34a, 34b, 34c and 34d respectively. The shorter arm of each filter carrier supports a guide pivot 35a, 35b, 35c and 3501 respectively. These guide pivots are guided in a curved guiding groove 33 of a filter setting ring 3'! rotatably disposed between the outer ring portion I" of ring I and the diaphragm setting ring 23. Ring 31 has eight detents 38a, 38a, 38b, 38b, 38c, 38c, 38d and 38:2 in its surface abutting against a face surface of ring portion l" of ring I. These detents are uniformly circumferentially spaced on a circle concentric with the axis of the objective mount. Ring portion I" of ring I is further provided with a bore 39 ending within the material of the ring and extending parallel to the axis of the objective mount. A ball 4| guided in bore 38 is engageable by means of a loaded spring as with the said detents 33a, 38a, 38b, 38b, 38c, 38c, 38d and 38d. The curved groove 36 of filter setting ring 31 is in the form of a circle concentric to the axis of the objective mount for the largest portion of its length but is flattened or otherwise bent inwardly in its section 35, as can best be seen on Fig. 2. The filter carriers 3m, 3Ib, 31c and 3ld, the guide pivots 35a, 35b, 35c and 35d of which are positioned in the circular section of curved groove 38 of the filter setting ring 3'! are outwardly pivoted so that the respective filters 34a, 34b, 34c and 34d are disposed outside the light beams between the lens components L2 and L3. If now ring 3! be rotated into a position so that one of the guide pivots 35a, 35b, 350 or 35d is located in the middle of the flattened section 36' of guiding groove 36, the respective filter carrier 3la, 31b, file or 31d is inwardly pivoted. As a result, the filter 34a, 34b, 340 or 3401 of the respective carrier is moved into a position concentric with the optical axis of the objective. It will now be apparent that by a rotation of the filter setting ring 31 through an angle of 45 in one or the other direction, the respective guide pivot 35a, 35b, 350 or 35d is moved out of section 36 of the curved groove whereby the respective filter carrier 3m, 3|b, 310 or 3id is again outwardly pivoted. The center angle defined by the ends of flattened section 36 of curved groove 36 is so selected that a guide pin 35a, 35b, 350 or 35d which is situated in the center of groove section 35' when filter setting ring 37 is in engagement with one of the detents, is moved completely out of groove section 35 by a rotation of ring 3? into an adjacent detent engaging position, that is through an angle of 45", without one of the adjacent guide pivots 35a, 35b, 350 or 35d entering groove section 36.

' Filter setting ring 37 has on its circumference four toothed portions 42a, 42b, 42c and 42d which divide the circumference of ring 31 in four equal sectors. As was previously explained, detents 38a, 38a, 38b, 38b, 38c, 38c, 38d and 38d provide for eight predetermined detained positions of ring 31. Accordingly, two filter setting indicia are marked in each sector of the circumference of ring 31. These indicia 43a, 43a, 43b, 43b, 43c, 43c, 43d and 43d coact with a marker 44 on the cylindrical surface of ring portion I" or ring 1 adjacent to filter setting ring 31. They also serve as setting marks for a diaphragm scale provided on the annular surface of diaphragm setting ring 23 adjacent to filter setting ring 31. The filter setting indicia 43a, 43b, 43c and 43d are each in form of a straight line parallel to the axis of the objective mount. When any one of these last mentioned indicia is in registry with marker M on ring section I" of ring 1, none of the filters is set for operation. The filter setting indicia 43a, 43b, 43c and 43d are each in form of a line twice bent at a right angle. The section of these bent indicia adjacent to ring portion l" of ring I serves for adjustment of filter setting ring 3'! relative to the filter setting marker 44. Consequently, when one of the said sections of the bent indicia 43a, 43b, 430 or 43d is placed in registry with the setting marker 34 the respective filter is set for use. The circumferential displacement of the section of each indicia 43a, 43b, 43c and 43d respectively relative to the indicia section used for setting of filter setting ring 3] corresponds to the time extension factor of the associated filter 34a, 34b, 34c and 31d. respectively. In other words, the aforesaid displaced sections of the indicia do not indicate on the diaphragm scale of the diaphragm setting ring 23 the diaphragm opening actually set but a smaller diaphragm opening which requires an exposure time corresponding to the exposure time of the actually set diaphragm aperture when taking in account the absorption of light by the operative filter 34a, 34b, 34c and 34d respectively.

In the modification according to Fig. 9, the bent filter setting indicia 43a, 43b, 43c and 43d are replaced by unbroken lines 45a, 45b, c and d each provided with a lateral radial extension 45a, 46b, 46c and 45d the length of which corresponds to the time extension factor of the respective filter 34a, 34b, 34c and 34d. The unbroken lines 45a, 45b, 45c and 45d indicate the actually set diaphragm opening on the diaphragm scale of diaphragm setting ring 23 and the ends of the extension lines 46a, 46b, 45c and 48d indicate the diaphragm opening which must be taken in account when the exposure time is to be ascertained by reason of the absorption of light by the filter 34a, 34b, 340 or 34d set in its position of use.

It may be advantageous to color the filter setting indicia 43a, 43b, 43c and 43d in accordance with the associated filters 34a, 34b, 34c and 34d respectively. The filter setting indicia 45a, 45b, 45c and 45d with their extensions 5.511., 462), 83c, 46d may also be accordingly colored. It is also possible to mark the color of each filter next to the respective setting mark on the filter setting ring 31 or the sectors of the filter setting ring 31 can be colored in accordance with the colors of the associated filters.

In certain instances it is desirable to provide so many different filters that the disposition of these filters in one plane may cause difiiculties. In such case the filters can be arranged in two groups that are axially displaced relative to each other.

Figs. 10 and 11 show an arrangement of this type for six filters and the means for selectively setting the same. The general arrangement and the operation of the objective mount according to Figs. 10 and 11 correspond to the arrangement and the operation of the objective mount according to Figs. 1 to 9 and the corresponding components are designated by the same numerals though increased by 100.

There are provided six filter carriers I3Ic, I3 Ib, I3Ic, I3Id, I3Ie, and I3If each in form of a bell crank lever. The longer arm of each carrier supports one of six different fitlers I3 la, I341), I340, I34d, I34e and I3. Each filter carrier is pivotally guided by means of a pivot pin 132a, I321), I320,,I320Z, I32e and I32f respectively which pivot pins engage bores I301), I331), I360, ISM, I33e and I331 respectively in the base of an annular groove I03 of the bearing ring IBI. The shorter arm of each filter carrier supports a guide pivot I35a, I351), I35c, I35d, I35e and I351 respectively. All these .guide pins are guided in a curved groove I33 of a filter setting ring I31 which is rotatably mounted between the outer portion IIlI of bearing ring IGI and a diaphragm setting ring I23. The filter setting ring 131 has in its surface abutting against the end surface of outer portion I02 of bearing ring I3! twelve detents I38a, I38a', I381), I381), I380, I380, I38d, I38d, I38e, I38e, I38) and I38? which are uniformly distributed on the circumference of a circle concentric with the axis of the objective mount. The outer ring portion I3I" is further provided with a bore I39 parallel to the axis of the objective mount and ending within the material of ring IBI. A ball MI is guided within this latter bore and biased by a loaded spring I43 toward engagement with one of the detents. The curved groove I36 of filter setting ring I31 is generally in form of a circle concentric with the axis of the objective mount but provided with a flattened portion I36.

Those filter carriers I3Ic, I311), I3Ic, I3Id, I3Ie and I3If, the guide pivots I35a, I351), I350, ISEcZ, I35e and I351 of which are positioned within the circular portion of the curved groove I36 01 the filter setting ring I31 are outwardly pivoted so that the filters 13411, I341), I340, IS Id, I34e and I341 supported by them are located outside the light beams between the lens components L2 and L3.

If new the filter setting ring I31 is rotated into a position in which one of the guide pivots 1350., i331), I350, I35c1, I356 or I35 is positioned in the middle or the flattened groove section I33 of g -ocve I33, the respective filter carrier 13m, i311), I3Ic, IBid, I3Ie or I3If i inwardly pivoted so that the filter supported by the respective filter carrier is moved into a position concentric with the optical axis of the objective mount. The center angle defining groove section I33 is so selected that a guide pivot I35c, i351), I350, 135d, I355 or i35f positioned in the middle of flattened groove section 533 when filter setting ring [31 is in one of its detained positions is moved completely out of the groove section I33 upon rotation of the fiiter setting ring I31 into an adjacent position, that is, through an angle of A continued rotation of the filter setting ring I31 through an angle 30 and in the same direction then moves the next following guide pivot 135a, i351), i330, Id, 1315c or $35 into the middle of groove section 533.

The longer arm offilter carriers I3Ic, .13 I1), 1310, 135d, 13Ie and 3If each of which supports one of the filters I'36a, I341), i340, 134d, Hide and i337 istwice bent ofi at a right angle and each ionger arm reaches through a slot M311, 1331), I330, 533d, i33e and 3133f respectively in the base of the :an-

nular groove I03 of bearing ring .IIII and through corresponding openings I33a, I331), I330, I33d', I33e and I33 respectively of a bearing ring member I33 into the space between the rings I06 and IE1 and between the lens components L2 and L3 respectively.

The filter carriers I3Ic, I3I1), I3Ic, I3Id, I3Ie, and I3lf with the filters I341, I34b, I340, I33d, I3 ie and I33 are divided in two groups, one group including the filter carriers I3Ic, I3Ie and I3Ie with the respective filters and the other group the filter carriers I3I1), I3Id and I3 I f with the respective filters. The pivot pins I32a, I320 and I326 of the filter carriers I3Ic, I3Ie and I3Ie are each provided with a distance or focusing ring I 32a, I320 and I32e respectively which rings abut against the base of annular groove I33 and serve to space the filter carriers I3Ic, I3Ie and i3Ie from the base of the annular groove I33 of bearing ring 135. The pivot pins I321), I321! and [32 are not provided with such distance or focusing rings so that the respective filter carriers 13H), I3 Id and I3 If abut directly against the base of annular groove 133. The distance between a pivot pin and the first bent-ofi portion of the respective filter carrier is somewhat larger with the filter carriers 131a, 13:0 and I3Ie than it is with the filter carriers S3Ib, I3id and I3If so that the section Of the filter carriers I3 ia, I3 Ic, I3Ie which is parallel to the optical axis of the objective mount is somewhat closer to this axis than the corresponding section of filter carriers I3 I1), I3Id and 13h. As a result, adjacent filter carriers can be pivoted without interfering with each other. The section of the filter carriers 53I1), I3id, I3If parallel to the axis of the objective mount is slightly longer than the corresponding section or the filter carriers I3Ic, I3Ie and I3Ie so that the filters I331), I33d, and I331 are axially displaced toward the camera side of the objective relative to the filters I34a, i330 and I3 ie. As a result, the filter carriers and filters do not interi'ere with each other when pivoted.

The filter setting ring I31 is provided on its circumference with six toothed portions I lZa, H121), I320, 132d, I32e and I42 which divide the circumference of the filter setting ring I31 in six equal sectors. As previously explained, detents E3341, i331), I380, 138d, I33e and I33) provide for twelve predetermined detained positions of filter setting ring I31. Accordingly, two filter setting indicia are marked in each sector of the circumierence of ring I31. These indicia I33a, I43a', i331), I431), M30, M30, I43d, I43d, 133e, I436, I43f and I331" coact with a marker I 33 on the cylindrical surface of ring portion I3I of bearing ring I32. They also serve as setting marks for a diaphragm scale provided on the annular surface 525 of the diaphragm setting ring I23 adjacent to filter setting ring I31. The filter setting indicia I33a, I631), I330, H3311, Ifi3e and I43) are each in form of a straight line parallel to the axis of the objective mount. When any one of these last mentioned six indicia is in registry with marker I64. on ring section IUI" of ring itl, none of the filters is set for operation. The filter setting indicia 1 33a, I331), i330, H5311, 533a and H23 are each in form of a line twice bent at a right angle. The portion of these bent indicia adjacent to ring portion IIlI" serves for adjustment of filter setting ring I31 relative to the filter setting mark 143. Consequently, when one of the said sections of the bent indicia I43a, I331), I430, -Id3d, I330 and I33 is placed in registry with the setting marker 144, the respective filter l34a, [3 5b, I340, 13411, [346 or I341 is set for use. The circumferential displacement of the portion of each indicia 143a, l43b, I430, M311, Mite and 143]" relative to the indicia section that is used for setting of filter setting ring I 3'! corresponds to the time extension factor of the associated filter 134a, l34h,'l3tc, NM, [346 and I34 respectively, as has been fully described in connection with Figs. 1 to 9 inclusive.

While the invention has been described in detail with respect to certain now preferred examples and embodiments of the invention it will be understood by those skilled in the art after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a mount for photographic objectives with built-in filters selectively movable into a use position concentric with the optical axis of the objective, two rings disposed within the mount concentric with the optical axis of the objective, one of said rings being fixedly and the other rotatably mounted, a plurality of carriers carrying difierent filters having different time extension factors pivotally supported on one of said rings in positions circumferentially spaced about the said optical axis, and control means controlled by the relative rotational position of the two rings and operatively coupled with each of said filter carriers for selectively pivoting, by a rotation of the rotatable ring, any one of said filter carriers either into the use position or into a position outside the incident light beams through the objective, the said control means comprising a guide pin extending from each of the filter carriers pivotally supported on one of said rings, the other ring being formed with an annular guiding groove concentric with the optical axis of the objective and including a non-concentric bent-in section, the said guide pins engaging said guiding groove for controlling the pivotal positions of the filter carriers by the positions of the guide pins in the guiding groove, a filter carrier the guide pin of which engages said non-concentric groove section being in the use position and a filter carrier the guide pine of which engages the concentric groove section being in the position outside the incident light beams through the objec tive.

2. An objective mount as defined in claim 1, wherein the said filter carriers, the said guide pins and the said guiding groove are arranged in a spatial relationship in which not more than one guide pin can occupy said non-concentric guiding groove section whereby all the filter carriers save one are always in the said outside position.

3. An objective mount as defined in claim 2. wherein the center angle defined by the circumferential ends of the non-concentric groove section is of such width that when a guide pin cccupies about the center of the said section the associated filter carrier is in its use position and that the said guide pin is moved into concentric section of the groove whereby the respective iiter carrier is in its outside position before the guide pin of an adjacent filter carrier is moved into the non-concentric groove section in response to a relative rotation of the rings' 4. An objective mount as defined in claim 3, wherein a plurality of yieldable detent means are provided between the adjacent sides of said rings for yieldably retaining the said rings in a selected one of several predetermined relative positions.

5. An objective mount as defined in claim 4, wherein the said yieldable detent means comprise a plurality of circumferentially spaced notches formed in the respective side of one of the rings, a bore formed in the respective side of the other ring, and a spring loaded detention element in the said bore engageable with said notches.

6. An objective mount as defined in claim 5, wherein the number of said notches is twice the number of said filter carriers, and wherein the said notches are circumferentially so spaced that a guide pin positioned in alignment with the line bisecting the said center angle when the two rings are in one of said detained relative positions is moved out of the non-concentric groove section upon rotation of the rotatable ring through the distance of the spacing between two adjacent notches and that the guide pin of one of the adjacent filter carriers reaches the said position of alignment upon a further rotation of the rotatable ring through the distance of a second notch spacing,

7. An objective mount as defined in claim 1, wherein the ring supporting the filter carriers also supports the objective, the other ring including said guiding groove being rotatably mounted upon said objective support ring for setting the pivotal filter carriers by rotating the said other ring.

8. An objective mount as defined in claim 7, in combination with a diaphragm oi? the iris type including relatively movable leaves, a ring rotatably mounted upon the ring supporting the objective adjacent to the filter carrier setting ring and operatively coupled with the leaves of the diaphragm for setting the opening of the latter, the said diaphragm setting ring having thereon a diaphragm scale calibrated by uniformly spaced indicia, the circumference of the filter carrier setting ring being divided in sectors correspond ing in number to the number of filter carriers, each sector including two indicia indicative of the setting of the filter carriers and also of the diaphragm opening, the said objective support ring having on a surface portion adjacent to the filter carrier setting ring a marker coasting with the said indicia included in the sectors, one of the two indicia of each sector being indicative of a position of the filter carrier setting ring in which none of the filter carriers is in the use position, the other of the said two indicia of each sector being indicative of a position of the filter carrier setting ring in which the respective filter carrier is in the use position and also indicating on the diaphragm scale of the diaphragm setting ring the time extension factor of the filter carried by the filter carrier in the aforesaid use position.

9. An objective mount as defined in claim 8, wherein the indicia on the scale of the filter carrier setting ring are diiferently colored in conformity with the filters carried by the respective associated filter carriers.

10. An objective mount as defined in claim 8, wherein the indicia on the filter carrier setting ring indicative of the positions of the filter carriers are in form or" a line twice bent-off at a right angle, the parallel portions of the said line 11 being displaced relative to each other in accordance with the time extension factor of the filter carried by the respective filter carrier.

11. An objective mount asdefined in. claim 9, wherein the indicia on the filter carrier setting ring indicative of the positions of the filter carriers are in form of a. straight line with a lateral extension thelength of which extension represents the time extension factor of the filter carried by the associated filter carrier.

12. An objective mount as defined in claim 1, wherein the said filter carriers, are arranged in two groups axially displaced on the axis of the objective mount and circumferentially placed 12 about the said axis, the filter carriers of the said two groups being so staggered relative one to another, that a filter carrier of one group alternates with a filter carrier of the other group.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 562,642 MacDonough June 23, 1896 1,766,637 Hopewell- June 24, 1930 2,185,847 Harrison et a1. Jan. 2; 1940 2,195,166 Digging Mar. 26, 1940 2,386,878 Nickerson Oct. 16, 1945 

